The proposal would not completely eliminate MATS, which sets limits on power plant emissions of mercury and other toxic pollutants. But it is “designed to put in place the legal justification for the Trump administration to weaken it and several other pollution rules,” and could open the door to a possible full repeal of the regulation, according to The New York Times.

Considered by the World Health Organization to be one of the Top 10 chemicals of major public health concern, mercury is a potent neurotoxin that can cause brain damage in young children, among a slew of other negative health effects. High levels of mercury also adversely affect wildlife.

As the Post reported, Robert Murray, chief executive of the Murray Energy Corporation, one of the country’s largest coal companies, personally requested the repeal of MATS in a letter to Energy Secretary Rick Perry last year.

Andrew Wheeler, who was retained for years as a lobbyist for Murray Energy, is the current acting administrator of the EPA. He directed the agency in August to “reconsider” the mercury rule.

The Trump administration is making a major move to eliminate regulation of a highly toxic chemical emitted from coal-burning plants — one known to be hazardous to children and fetuses. https://t.co/hfXAL2Vp0Y

The new proposal would reportedly reverse a 2011 Obama administration finding that the EPA must take indirect health benefits ― known as “co-benefits” ― into account when evaluating the costs and benefits of toxic pollution regulations.

In the case of MATS, for example, the Obama administration estimated that the rule would cost industry $9.6 billion a year ― making it one of the most expensive regulations that the EPA had ever issued. The administration argued, however, that the costs were far outweighed by the rule’s enormous health benefits.

“It found that reducing mercury brings up to $6 million annually in health benefits — a high number, but not as high as the cost to industry,” the Times explained. “However, it further justified the regulation by citing an additional $80 billion in health benefits”― in other words, “co-benefits” ― from the reduction in hazardous soot and nitrogen oxide that occurred as a side effect of limiting mercury emissions.

Under the new proposal, the EPA would no longer need to consider such “co-benefits” when determining the net cost of a regulation, the Times reported.

If the proposal is approved, therefore, the health benefits of MATS ― at least on paper ― would no longer outweigh its economic cost, leaving it vulnerable to weakening or even repeal. (Both the Post and the Times noted that Brett Kavanaugh, President Trump’s embattled Supreme Court nominee, would likely vote to toss out the rule. Kavanaugh expressed skepticism in an earlier opinion about the benefits of MATS.)

Environmental groups and activists have reacted with horror at the news of the proposed rule.

“Are pro-life evangelicals fine with the Trump administration attacking safeguards against mercury & lead pollution that damages the developing brains & nervous systems of fetuses & children?” John Walke, clean air director of environmental advocacy group Natural Resources Defense Council, wrote in a Monday Twitter post.